Voltage regulator circuit



Patented Apr. 18, 1950 VOLTAGE REGULATOR CIRCUIT Robert M. Tryon, Compton, Calif., assignor to Radio Corporation of America, a corporation Delaware Application April 24, 1948, Serial No. 22,987

9 Claims.

This invention relates to voltage regulator circuits, and particularly to a voltage supply for developing a regulated low output voltage of constant value suitable for supply grid bias to an amplifier tube.

Conventional voltage regulator circuits are known which include a variable resistance tube connected either in shunt or in series with the load. Theresistance of the tube is varied by a control voltage responsive to variations of the input or output voltage, or both, so as to maintain the load voltage substantially constant. Thus, voltage control is effected in a conventional voltage regulator circuit by controlling the amplification of a vacuum amplifier tube in shunt with the load in accordance with variations of the input and of the output voltage derived from separate shunt resistors. The shunt resistors are usually connected to one or .more control grids, and the cathode potential is maintained at a fixed value which must be above the grid potential to provide the normal bias voltage between cathode and control grid of the tube. To this end, a constant-voltagedrop tube must be provided in the cathode circuit in series with the shunt regulator tube. The voltage across both tubes which is the output voltage, is accordingly comparatively high, that is, of the order of 100vo1ts or more. A

voltage regulator of this type has been disclosed a in the patent to Keizer 2,372,432 granted on March 27, 1945.

Therefore, when a regulated voltage of the order of 30 volts is required, conventional voltage regulator circuits cannot be used. Such a regulated low voltage may be needed for supplying grid bias voltage to certain of the tubes used in various types of equipment. Examples .of such equipment are the power amplifiers of a transmitter, certain oscillators, or an airborne television receiver wherein a pulse shaping network including vacuum tubes is required. In all these cases, the grid bias voltage of the tubes must be controlled within very narrow limits. The problem of providing a well regulated grid bias voltage becomes still more complicated when the tubes draw grid current periodically.

It is, accordingly, an object of the present invention to provide a voltage regulator circuit for developing a regulated low output voltage of 2 constant value which is not affected by variations in the output current.

A further object of the invention is to provide a regulated voltage supply which develops a regulated negative grid bias voltage suitable for tubes which periodically draw grid current and which requires a minimum of circuit elements and tubes.

A voltage regulator in accordance with the present invention comprises a source of voltage to be regulated across which a constant-voltagedrop tube is connected. The constant-voltagedrop tube may be a cold-cathode, glow-discharge voltage regulator tube for maintaining the voltage across the voltage source substantially constant. An impedance element such as a dropping resistor is provided in series between the voltage source and the load impedance. Finally, a variable resistance device such as a space discharge tube is connected in shunt with the voltage source, that is, between the junction point of the dropping or series resistor and load impedance and one terminal of. the voltage source. Consequently, the variable'resistance device is responsive to voltage variations across the series resistor and functions to regulate the voltage across the load impedance.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organiza tion and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing, in which the single figure is a schematic circuit diagram of a voltage regulator circuit embodying the present invention.

Referring now to the drawing, there is illustrated a voltage regulator circuit com-prising a voltage source I which is to be regulated. An alternating voltage is impressed on the primary 3 of transformer 2. The two terminals of the transformer secondary winding 4 are connected to rectifiers *5, 6 forming part of a conventional full-wave rectifier circuit. Rectifiers 5, 6 may be selenium or other dry rectifiers as indicated, or any other type of rectifier such as a vacuum diode may be used. The output electrodes of rectifiers 5, G are connected through resistors I, 8, respectively, to negative output lead III. The mid-point of secondary winding 4 is grounded as shown.

Voltage source I may also be provided with a conventional filter network including series choke coil I2 and shunt capacitors I3, I conlnected between negative output lead I and ground. The negative output voltage to be regulated is obtained between negative output lead I0 and ground. While a conventional power supply rectifier-filter source has been illustrated, it is to be understood that the principles of this invention may be applied to the control of any source of direct current voltage which requires regulation.

Constant-voltage-drop tube I5 is connected in shunt across voltage source I, that is, between negative output lead I9 and ground. A series resistor I6 may be provided between voltage source I and constant-voltage-drop tube I5 to limit the current which may flow through tube I5. It is to be understood that, it voltage source I has a sufficiently high impedance, resistor I6 may be omitted. Constant-voltage-drop tube I5 may be of the cold-cathode, glow-discharge type. Thus, constant-voltage-drop tube I5 may, for example, be a gaseous voltage regulator tube of the VR type. Preferably tube I5 is of the VR 75 type which has a voltage drop thereacross of '75 volts only; this is the smallest voltage drop available for a gaseous voltage regulator tube. These voltage regulator tubes have the unique property that, within the operating limits of the tube, the voltage drop across the tube is constant, regardless of the current flowing through the tube. Consequently, the resistance 01' a voltage regulator tube of the VR type varies linearly and inversely with the applied voltage.

In accordance with the present invention. resistor I I is provided in series between voltage source I or resistor I6, and the utilization device or load whose impedance may vary, as represented by variable load resistor I8. Dropping resistor I1 is provided for the purpose of reducing the voltage across constant-voltage-drop tube I5 which may amount to -75 volts, to a value of approximately 30 volts with respect to ground. A variable resistance device such as vacuum tube 20 is connected between the junction point of series resistor I1 and load resistor I8 and ground. Vacuum or space discharge tube 20 may be a triode comprising cathode 2I, control grid 22 and anode 23. Anode 23 is connected to ground, while cathode 2| is connected to the junction point between series resistor I1 and variable load resistor I8.

Constant-voltage-drop tube I5 is shunted by resistor 24 which forms a voltage divider having a variable tap 25 connected to control grid 22. Control grid 22 may be bypassed to ground by bypass condenser 26. Bypass condenser 21 bypasses triode 20 to ground.

The voltage regulator circuit of the invention operates as follows. Anode 23 of triode 20 is maintained at a fixed potential, that is, at ground potential. Control grid 22 is also maintained substantially at a fixed potential with respect to ground or anode 23 because the voltage between the junction point of resistors I6, I1 and ground is maintained substantially constant by constant voltage drop tube I5. Thus, the voltage of control grid 22 may, for example, be 31 volts and that of cathode 2I may be -30 volts with respect to ground. Accordingly, the input voltage of the voltage regulator, that is, the voltage between 4 the input terminal of series resistor I1 and ground, is maintained substantially constant at a value of '75 volts which, however, is higher than the desired output voltage.

Let it be assumed that the current through variable load resistor l.- increases, that is, the resistance of resistor I8 decreases. In that case. more current will flow through series resistor I1. and the voltage of cathode 2I will become less negative with respect to that of control grid 22. This will increase the negative bias voltage of control grid 22 with respect to cathode 2I, and consequently, the current through triode 20 will decrease. This, in turn, will compensate for the larger current flowing through variable load resistor I8 and accordingly the current flowing through series resistor I! will be maintained substantially constant.

On the other hand, when the current through variable load resistor It decreases, that is, when the resistance 01' resistor I8 increases, less current will flow through series resistor I1 and cathode 2I will be driven more with respect to its grid 22, with a consequent reduction of the negative bias voltage of control grid 22 with respect to cathode 2I. This, in turn, will increase the current through triode 20 and, again, the total current flowing through series resistor II will be maintained substantially constant.

It will, therefore, be seen that constant voltage drop tube I5 simultaneously functions to maintain the input voltage 01' series resistor II constant and to supply a fixed voltage to control grid 22. Thus, only the voltage of cathode 2I is allowed to vary in response to variations of the load current. Triode 20 therefore functions as a degenerative amplifier and its resistance is controlled in response to voltage variations across series resistor I'I. Bypass condenser 26 will remove any variations oi the voltage between control grid 22 and ground, while bypass condenser 21 will bypass short time variations in voltage between cathode 2I and ground.

The voltage regulator circuit of the present invention is particularly suitable for supplying a regulated negative voltage of the order 0! 30 volts. Although it will be understood that the circuit specifications of the regulated voltage supply or the invention may vary according to the design for any particular application, the following circuit specifications are included, by way of example only, as suitable for supplying a negative voltage of 30 volts:

Constant voltage drop tube I I VR Space discharge tube 20 (connected as a triode) 6AQ5 Series resistor I8 ohms 2,500 Series resistor I1 do 2,700 Resistor 24 do 25,000 Bypass condenser 28 microfarad .25 Bypass condenser 21 do .75

In a circuit with the above specifications the nominal current through load resistor It was 05 9 milliamperes and this current varied no more Space discharge tube 20 preferably is a triode or a multigrid tube connected as a triode, such as a 6AQ5 type pentode.

There has thus been described a voltage regulator circuit which will develop a regulated low output voltage of negative polarity. The regulated low output voltage is suitable for supplying a grid bias voltage of substantially constant magnitude to an amplifier tube which periodically draws grid current. The circuit requires only a minimum of circuit elements and tubes.

Another feature of the voltage regulator aircuit of the invention is that a shunt tube is used for regulating the voltage across the load which has its cathode voltage varied in accordance with variations of the voltageacross a resistor arranged in series with the load. The shunt tube hence functions as a degenerative amplifier. This arrangement makes it possible to obtain a regulated low output voltage by means of a vacuum tube.

What is claimed is:

1. A voltage regulator circuit comprising a source of voltage to be regulated, a load impedance element, a second impedance element connected in series with said load impedance element and said source, a degenerative amplifier having a cathode, an anode and a grid, means for maintaining said anode at a fixed potential, means including a constant-voltage-drop tube connected across said source for maintaining said grid at a substantially fixed potential which differs from that of said anode, and a connection between said second impedance element and said cathode to vary the potential of said cathode in accordance with voltage variations across said second impedance element.

. grid including a constant-voltage-drop tube connected across said source for maintaining said grid at a substantially fixed potential which difiers from that of said anode, and a connection between said second impedance element and said cathode to render the flow of current through said amplifier responsive to voltage variations across said second impedance element.

3'. A voltage regulator circuit comprising a source of voltage to be regulated, a constantvoltage-drop tube connected across said source to maintain the voltage thereacross substantially constant, a load impedance element, a second impedance element connected in series with said load impedance element and said source, and a variable resistance device connected in shunt with said source and having two cooperating resistance controlling elements coupled respectively to said constant-voltage-drop tube and to said second impedance element, whereby to render said device responsive to voltage variations across said second impedance element to regulate the voltage across said load impedance element.

4. A voltage regulator circuit comprising a source of voltage to be regulated, a constantvoltage drop tube connected across said source to maintain the voltage thereacross substantially constant, a load impedance element, a second impedance element connected in series with said load impedance element and said source, and a variable resistance device comprising a space discharge tube connected between the Junction point of said elements and said source, said device having two cooperating resistance controlling electrodes, one of said electrodes being coupled to said constant-voltage-drop tube and the other electrode being coupled to said second impedance element, whereby to render said device responsive to voltage variations across said second impedance elementto regulate the voltage across said load impedance element.

5. A voltage regulator circuit comprising a source of voltage to be regulated, a constantvoltage-drop tube connected across said source to maintain the voltage thereacross substantially constant, a load impedance element, a second impedance element connected in series with said load impedance element and said source, a variable resistance space discharge tube having a cathode, a control grid and an anode, said cathode and anode being connected between the junction point of said elements and said source, and a voltage divider including said constant-voltagedrop tube connected to said control grid, whereby said space discharge tube is responsive to voltage variations across said second impedance element to regulate the voltage across said load impedance element.

6. A voltage regulator circuit for deriving a negative regulated voltage comprising a source of voltage to be regulated, a constant-voltagedi'op tube connected across said source to maintain the voltage thereacross substantially constant, a load impedance element, a resistor connected in serie with said load impedance element and said source, a variable resistance space discharge tube having a cathode, a control grid and an anode, said cathode being connected to the junction point of said resistor and said element, said anode being connected to said source, and a voltage divider shunted across said constantvoltage-drop tube and connected to said con: trol grid, whereby said space discharge tube is responsive to voltage variations across said resistor to regulate the voltage across said load impedance element.

7. A regulated voltage supply comprising a source of voltage to be regulated, a constantvoltage-drop tube connected across said source, a space discharge tube having a cathode, a control'grid and an anode, an impedance element connected in series between said cathode and one terminal of said source, the other terminal of said source being connected to said anode, and a potentiometer including said constant-voltagedrop tube for supplying a substantially constant potential to said grid, whereby the current through said space discharge tube varies with variations of the voltage across said element.

8. A regulated voltage supply comprising a source of voltage to be regulated, a constantvoltage-drop tube connected across said source, a vacuum tube having a cathode, a control grid and an anode, an impedance element connected in series between said cathode and one terminal of said source, the other terminal of said source being connected to said anode, and a potentiometer connected across said constant-voltagedrop tube for supplying a substantially constant potential to said grid, whereby the resistance of said vacuum tube is responsive to variations of the voltage across said element.

9. A regulated voltage supply comprising a source of voltage to be regulated, a constantvoltage-drop tube connected across said source. REFERENCES CITED a vacuum tube having a cathode. a control grid an mode, a resistor connected in series my: folloaggtgeraeierences are of record in the tween said cathode and one terminal of said source. the other terminal of said source being 5 UNITED S ATES PATENTS connected to said anode, a potentiometer 0011- Number Name Date nected across said constant-voltage-drop tube. 1,835,121 Rentschler Dec. 8, i931 and an adjustable circuit connection between 2,409,151 Rogers ..Oct. 3, 1946 said potentiometer and said control grid for sup- 2,416,922 Irish Mar. 4, 1947 11191118 a substantially constant potential to said 10 grid. whereby the resistance of said vacuum tube is responsive to variations of the voltage across said resistor.

ROBERT M. TRYON. 

